An assembler is a type of computer program that translates assembly language, a low-level programming language, into machine code, which is the binary code that a computer's processor can execute. Assembly language uses mnemonics and symbols to represent machine-level instructions, making it easier for programmers to write and understand code compared to raw binary. Assemblers play a crucial role in software development, especially in systems programming and embedded systems, where performance and hardware control are essential. They help bridge the gap between human-readable code and machine-executable instructions, allowing developers to create efficient programs that interact directly with the hardware, such as microcontrollers and CPUs.